1. Field of the Invention
The invention is based on a compressed-gas breaker having two contact members, which can be brought into or out of engagement with one another along one axis, of which a first one is constructed as a nozzle and exhibits contact fingers elastically mounted on a tubular contact carrier, having an insulating nozzle and having a heating volume for storing switching-arc-generated compressed gas, in which, in the operated condition, a second one of the two contact members is conducted through the constriction of the insulating nozzle and is inserted, with a free end, into the first contact member whilst forming a contact force with the contact fingers, and in which, during interruption, compressed gas flows from the heating volume through the insulating nozzle and the first contact member into an exhaust space.
2. Discussion of Background
In this connection, the invention refers to a prior art of compressed-gas breakers described, for example, in DE-A No. 1-34 25 633. In the known compressed gas breakers, compressed gas is generated with the aid of the switching arc during the high-current phase during interruption and stored in a heating volume. When the current to be disconnected approaches a zero transition, the stored compressed gas removes energy from the switching arc by axial blasting and thus causes it to be extinguished. During this process, a considerable proportion of the compressed gas stored in the heating volume can already be removed, before the zero transition of the current, into the exhaust space of the breaker by means of a contact member constructed as a nozzle, depending on the magnitude of the current to be disconnected. The greater the cross-section of the nozzle, the greater this proportion of compressed gas removed from the heating volume. However, the nozzle cross-section is in most cases defined by particular boundary conditions such as, for example, contact erosion, insulating nozzle erosion and/or magnitude of the shortcircuit current to be disconnected. For these reasons, the known compressed-gas breaker exhibits a further constriction downstream of the nozzle constriction of the nozzle-shaped contact member in the embodiment according to FIG. 3. This further constriction closes off a volume which is limited by the upstream part of the contact member and which supports the heating power of the switching arc during interruption and causes a pressure increase in the heating volume. However, such a breaker does not exhibit an optimum thermal quenching capacity which is dependent on arc edge turbulences since the switching arc is now no longer conducted through the narrowest location in the compressed-gas flow at which the arc edge turbulences are at a maximum.